Purification of petroleum distillates



F -atented Apr. 30, 1957 PURIFICATION OF PETROLEUM DISTILLATES Curtis F.Gerald, Lake Zurich, Ill., assignor to Universal Oil Products Company,Des Plaines, Ill., a corporation of Delaware No Drawing. ApplicationFebruary 21, 1955, Serial No. 489,750

9 Claims. (Cl. 196-==23) This invention relates to the purification ofpetroleum distillates and more particularly to an improved method toremove nitrogen compounds from petroleum distillates.

Petroleum distillates contain sulfur compounds and nitrogen compounds.The nitrogen compounds generally are present in smaller concentrationsthan are the sulfur compounds. However, the nitrogen compounds, eventhough present in smaller concentrations, are objectionable for variousreasons and must be removed from the petroleum distillate. For example,certain petroleum distillates may be marketed under specifications whichrecite a maximum nitrogen content. In other cases, petroleum distillatesare subjected to conversion in the presence of catalysts which aredetrimentally affected by nitrogen compounds as, for example, noblemetal and particularly platinum catalysts, and the nitrogen content ofthe petroleum distillate must be reduced to below a certain maximum.Another example, nitrogen compounds adversely affect catalytic crackingand the removal of nitrogen compounds from the petroleum distillatecharge is desirable.

While the sulfur compounds appear to be readily removed by conventionaltreatment, the nitrogen compounds are much more diflicult to remove.This, in turn, requires moredrastic treatment of the petroleumdistillate to remove the nitrogen compounds and results in more rapiddeactivation of the catalyst. The present invention provides a novelmethod of avoiding the rapid deactivation of the catalyst and therebyprovides a more efiicient process for the removal of both nitrogenandsulfur compounds from petroleum distillates. In addition, any olefiniccompounds present in the petroleum distillate are hydrogenated to thecorresponding parafiinic hydrocarbons. Certain metallic impuritieslikewise are removed from the petroleum distillate in this process.

As hereinbefore set forth, the sulfur compounds gen erally are presentin greater concentrations than are the nitrogen compounds. ,However, inmany cases, the ratio of sulfur compounds to nitrogen compounds is notsufficient to provide the improved benefits. When treating suchdistillates improved nitrogen removal may be obtained by processing inaccordance with the teachings of the present invention.

In one embodiment, the present invention relates to .an improvement inthe removal of nitrogen from a petroleum distillate, containing nitrogenin a proportion to sulfur greater than hereinafter defined, by treatingwith hydrogen and a molybdenum containing catalyst at purificationconditions. The improvement comprises adding sulfur to said distillatein an amount that the total sulfuris in a concentration at least equalto that expressed by the equation S=25.8N+0.07l, where S is sulfur inweight percent and N is nitrogen in weight percent, provided howeverthat the total sulfur concentration is at least 0.2% by weight of saidpetroleum distillate.

As described herein, improved nitrogen removal is oblite, etc.

tained when the sulfur to nitrogen ratio is at least equal to thecritical concentration defined by the equation. The exact reason for theimproved results has not been definitely established, but is believed tobe related to the formation and/ or maintenance of one or moreparticular sulfided forms of the catalyst. Regardless of the exactexplanation, it appears necessary that at least a certain concentrationof sulfur is present and that such concentration of sulfur appearsrelated to the nitrogen content of the petroleum distillate.

The novel features of the present invention may be utilized for thepurification of any petroleum distillate containing nitrogen compoundsor nitrogen and sulfur compounds in a proportion greater than hereindefined. Thus, the present invention may be utilized for thepurification of gasoline, naphtha, aromatic solvent, kerosene, dieselfuel, gas oil, fuel oil, transformer oil, lubricating oil, etc., ormixtures thereof. While the invention is particularly applicable to thetreatment of petroleum distillates, it is understood that it may beutilized with other organic compounds containing the impurities asaforesaid and thus may be utilized for the treatment of liquidscomprising alcohols, aldehydes, ketones, acids, etc.

The catalyst for use in the present invention contains molybdenum.Generally the molybdenum will be associated with'a carrier or supportingmaterial, which material may be catalytically inert or may becatalytically inert or may be catalytically active, particularly inassociation with the molybdenum compound. Alumina is particularlypreferred for this purpose. Other supporting or carrying materialsinclude silica, zirconia, magnesia, zinc oxide, etc., or composites suchas silica-alumina, silica-magnesia, silica-zirconia,silica-alumina-magnesia, silica-alumina-Zirconia, silica-alumina-thoria,etc., which may be synthetically prepared and naturally occurring.

Generally the catalyst also will contain a compound of the iron groupmetals including cobalt, iron and nickel. Cobalt appears to beparticularly preferred.

The composited catalyst may be prepared in any suitable manner includingcoprecipitation, separate precipita tion or successive precipitationmethods. In the coprecipitation method, suitable compounds of aluminum,molybdenum and cobalt are commingled, and the oxides thereofprecipitated by the addition of a suitable precipitating agent, or theoxides are developed by heating, depending upon the particular compoundsof metals used in preparing the catalyst.

In separate precipitation methods, each component is precipitatedseparately and then commingled. In this method, the alumina may besynthetically prepared or it may comprise suitable naturally occurringaluminous materials including bauxite, diaspore, gibbsite, hydrargil-Usually the naturally occurring materials are acid or otherwise treatedin order to activate the same.

In successive precipitation methods, the oxides of one or more of thecomponents are precipitated, and suitable compounds of the othercomponent or components are cornmingled therewith and the oxide oroxides precipitated in the presence thereof. Here again it is understoodthat suitable naturally occurring alumina may be employed, again usuallywith acid or other treatment prior to use in the preparation of thecatalyst.

In the successive or separate precipitation methods, it is understoodthat the oxides may be developed by heating, depending upon theparticular metal compounds used in preparing the catalyst, and alsothat, in these methods, washing and/or drying between steps may beemployed.

When synthetically prepared alumina is employed, it generally isprepared by commingling a suitable basic compound, including ammoniumhydroxide, ammonium carbonate, etc., with an acidic compound ofaluminum, including the chloride, bromide, iodide, fluoride, sulfate,

phosphate, nitrate, acetate, etc., or it may be prepared by the additionof a suitable acidic compound, including hydrogen chloride, sulfuricacid, phosphoric acid, etc., to an alkaline compound of aluminum as, forexample, sodium aluminate, etc. ln other than coprecipitation methods,the resultant hydroxide of aluminum may be composited in the wet statewith the other components or it may be washed to remove solubleimpurities and/or dried at a temperature of from about 200- to about 600F. for a period of l to 24 hours or more and the composited with theother components.

The aluminum hydroxide or aluminamay be composited with the othercomponents of the catalyst in any suitable manner andeither separatelyor together. When separate compositing is employed, the intermediatecomposite may be Washed and/or. dried at intervening stages. In somecases, it may bedcsirable also to calcine at such intervening stages;that is, thealumina or the composition of alumina and one component iscalcined prior to compositing with the remaining components. Thecalcining generally is effected at a temperature of from about 600 to1600 F. or more for a period of from about 1 to 12 hours or more.

Any suitable compound of molybdenum may be employed and thus maycomprise molybdic acid, molybdenum trioxide, molybdenum tetrabromide,molybdenum oxydibromide, molybdenum tetrachloride, molybdenumoxydichloride, molybdenum oxypentachloride, molybdenum oxytctrafluoridc,etc. Similarly any suitablecompound of cobalt may be employed, includingcobalt nitrate hexahydrate, cobalt ammonium nitrate, cobalt ammoniumchloride, cobalt ammonium sulfate, cobalt bromide, cobalt bromate,cobalt chloride, cobaltchlorate, cobalt fluoride, cobalt fluorate, etc.

In a preferred method, either syntheticallyprepared or naturallyoccurring alumina, preferably after calcining, is composited withmolybdic acid, the resultant composite dried and calcined, after whichcobalt nitrate hexahydrate is commingled therewith, and the finalcomposite then is dried and calcined. It is understood that the dryingand calcining will be effected at the conditions hereinbefore set forth.In another method, the cobalt may be composited with the alumina andthen the molybdenum composited therewith. In still another method, anacidic impregnating solution of molybdic acid and cobalt nitrate isformed and this solution then is utilized to impregnate alumina. It isunderstood that the impregnation may be effected separately by utilizingdifferent acidic solutions of molybdic acid and of cobalt nitrate. Whendesired, the acidic solutions may contain nitric acid. hydrochloricacid. sulfuric acid, phosphoric acid, oxalic acid, etc., or mixturesthereof. While acidic impregnation is preferred, it is understood thatbasic impregnation, that is utilizing basic solutions or introducingsuitable basic reagents, either into the solution or onto the support,may be employed, the basic reagent includ ing, for example,ammoniumhydroxide, ammonium carbonate. alkyl amines, basic heterocyclicnitrogen compounds, etc.

While the preferred catalyst comprises a composite of alumina-molybdenumcompound-cobalt compound, it is understood that other supporting orcarrying materials may be employed as hereinbefore set forth, and alsothat the iron and nickel compounds may be utilized in place of or inaddition to the cobalt compoundbut not necessarily with equivalentresults. The iron and nickel compounds may be composited with thecatalyst in substantially the same manner as hereinbefore set forth forthe cobalt compound.

The components of the catalyst may be utilized in any suitableconcentration. In general, the cobalt or other iron group metal compoundand molybdenum compound will range from about 1% to 25% by Weight eachof final catalyst. Preferred catalysts contain the cobalt in 'aconcentration of from about 1% to about 210% :and the inum catalyst.

4 molybdenum in a concentration of from about 2% to about 20% by weightof final catalyst, the remainder comprising alumina.

Regardless of the specific method in which the catalyst is prepared, thefinal composite generally is calcined at a temperature of from about 600to about 1600 F. for a period of about 1 to 12 hours or more and usuallyin the presence of air, oxygen or other oxidizing-medium. In thisembodiment, the preferred catalyst comprises almarina-molybdenumoxide-cobalt oxide.

In another embodiment, the catalyst comprises alumina-molybdenumsulfide-cobalt sulfide, and this catalyst is readily obtained bysulfiding the oxide form of the catalyst. The sulfirlation may beeffected by passing hydrogen sulfide or other suitable sulfur compoundthrough the catalyst, preferably at a temperature of from about 400 toabout l000 F., until sulfidation is complete, which isreadily determinedwhen absorption of hydrogen sulfide or other sulfur compound ceases. Inanother embodiment, the oxide catalyst may be utilized for thepurification of sulfur containing organic compounds and the sulfidationis effected in situ.

While the alumina-molybdenum compound-cobalt compound catalyst isparticularly preferred, it is under stood that, in some cases, thecatalyst may contain additional components. For example, halogen may beincluded in the catalyst. The halogen may comprise fluorine, chlorine,iodine and/or bromine, and generally will be present in the catalyst ina combined form. The halogen may be introduced into the catalystseparately or in commingled state with one or more of the othercomponents as, for example, by utilizing a hydrogen fluoride or hydrogenchloride solution of molybdic acid and cobalt nitrate as theimpregnating solution. The halogen may be employed in a concentration offrom about 0.2% to 15% or more by Weight of the final catalyst.

The purification of petroleum distillates in the presence of a catalystcontaining molybdenum-compound, and particularly alumina-molybdenumoxide-cobalt oxide, is effected at a temperature of from about 400 to800-850 F. and a pressure of from atmospheric to 2000'pounds or more,particularly in the presence of hydrogen, the hydrogen being utilized ina molar ratio to hydrocarbon of from about 0.2:] to about 20:1.

As an essential feature of the present invention, when the petroleumdistillate contains nitrogen compounds and substantially no sulfurcompounds or both of these types of compounds but in a ratio of sulfurcompounds to nitrogen compounds less then that defined by the equationhereinbefore set forth, sulfur is added to the reaction in order thatthe concentration of sulfur is at least equal to that defined by theequation. duced in any suitable form including free sulfur,hydrogensulfide, carbon disulfide,thiophene, mercaptan, etc., and convenientlyis comrningled with the petroleum distillate prior to heating andintroduced along with the distillate into the reaction zone, or it maybe supplied directly to the reaction zone in any suitable manner. Ashereinbefore set forth, it is believed that the activity of the catalystis dependent upon a sulfided form and, therefore, requires the presenceof a critical amount of sulfur in order to maintain the desiredactivity. This critical concentration is related to the nitrogen chargedto the reaction zone and also must be above a critical minimtun. Theconcentration of sulfur with relation to nitrogen is expressed by the"equation S=25.8N+0.071, and the critical minimum is maintained byproviding at least 0.2% by weight of sulfur based on the petroleumdistillate. The sulfur-is calculated as'free sulfur-even though it maybe introducedin a combined form.

As hereinbefore set forth, the purification of the petroleum distillateis particularlydesirable when the pe troleum distillate subsequently issubjected to conversion in the presence of a noble metal andparticularly a plat- In this embodiment, the present inven- The sulfurmay be introtion may comprise a combination process wherein thepurification is efiected in the manner hereinbefore set forth and thethus purified gasoline or naphtha is subjected to reforming in thepresence of a reforming catalyst, the reforming being defined as atreatment of gasoline or naphtha to improve the antiknockcharacteristics thereof. In the reforming reaction, hydrogen is producedand the hydrogen thus produced is utilized in part in the purificationtreatment and in part in the reforming step. A particularly suitablecatalyst for the reforming reaction comprises .alumina-platinum-combinedhalogen. Other catalysts include silica-alumina-platinum,silica-magnesia-platinum, silica-zirconia-platinum, etc., which catalystmay contain halogen when desired. The platinum generally is utilized ina concentration of from about 0.05 to about 1% by weight of the finalcatalyst and the halogen, when employed, is utilized in a concentrationof from about 0.1 to about 5-10% by weight of the catalyst. Thereforming is effected at a temperature of from about 800 to about 1100F. and a pressure of from about 100 to 2000 pounds or more, in thepresence of hydrogen in a mol ratio to hydrocarbon of from about 0.2:1to :1 or more.

Purification of the petroleum distillate or other organic compound withadded sulfur may be effected in any suitable manner, including a fixedbed type of operation in which the charge is passed at the desiredtemperature and pressure through the catalyst, in either upward ordownward flow, and the efiiuent therefrom is fractionated or otherwisetreated to recover the desired product. When the process is efiected inthe presence of hydrogen, it may be preferred to recycle at least aportion of the excess hydrogen for further use in the process. In placeof the fixed bed operation, other operations may be used, including thefluidized type in which the charge and catalyst are maintained inturbulent fiow within the reaction zone, the slurry or suspensoid typeof operation in which the catalyst and charge are transported as aslurry into the reaction zone, the moving bed type of process in whichthe catalyst moves as a mass either concurrently or countercurrently tothe charge, etc.

Although the catalyst of the present invention will have a long life, itmay require regeneration after a long period of service, and theregeneration may be effected in any suitable manner. In one method,regeneration of the catalyst may be effected by burning carbonaceousdeposits with air or other oxygen-containing gases. In some cases,regeneration of the catalyst may be effected by treatment at hightemperatures with hydrogen or other gases and, in other cases, both ofthese methods may be employed.

The following examples are introduced to illustrate further the noveltyand utility of the present invention but not with the intention ofunduly limiting the same.

In this example a selected charge stock was utilized in order tospecifically determine the effect of nitrogen and sulfur compoundstherein. The charge comprised solvent naphtha to which was added 956parts per million of nitrogen as quinoline and 0.2% by weight of sulfuras thiophene. The charge had an API gravity at 60 F. of 53.6. Thecatalyst comprised alumina, about 7% by weight of molybdenum sulfide andabout 3% by weight of cobalt sulfide. The charge was subjected topurification at a temperature of about 700 F. and a pressure of about800 pounds per square inch in the presence of about 3000 cubic feet ofhydrogen per barrel of petroleum distillate.

In the run described above, the product contained about 32 parts permillion of basic nitrogen. It will be noted that the nitrogen content ofthe product is too high for many purposes. Also, it will be noted thatthe amount of sulfur in relation to the nitrogen is below that requiredby the equation. According to the equation S=25.8N+0.071, the minimumconcentration of sul- 6 fur should be about 0.32. When sulfur is addedto the charge to give a concentration of at least about 0.32% sulfur andthe charge subjected to purification as aforesaid, the product will havea basic nitrogen content of below about 5 parts per million.

i claim as my invention.

1. In the removal of nitrogen from a petroleum distillate containingnitrogen in a proportion to sulfur greater that hereinafter defined, bytreatment at purification conditions in the presence of a molybdenumcontaining catalyst, the improvement which comprises adding sulfur tosaid distillate in an amount such that the total sulfur is inconcentration at least equal to that expressed by the equationS=25.8N+0.071, where S is sulfur in weight percent and N is nitrogen inweight percent, provided, however, that the total sulfur concentrationis at least 0.2% by Weight of said petroleum distillate.

2. In the removal of nitrogen from a petroleum dis tillate containingnitrogen in a proportion to sulfur greater that hereinafter defined, bytreating with hydrogen and a catalyst comprising alumina and molybdenumcompound at purification conditions, the improvement which comprisesadding sulfur to said distillate in an amount such that the total sulfuris in a concentration at least equal to that expressed by the equationS=25.8N-|-0.071, where S is sulfur in weight percent and N is nitrogenin weight percent, provided, however, that the total sulfurconcentration is at least 0.2% by weight of said petroleum distillate.

3. In the removal of nitrogen from a petroleum distillate containingnitrogen in a proportion to sulfur greater than hereinafter defined, bytreatment with hydrogen and a catalyst comprising alumina-molybdenumsulfide-cobalt sulfide at a temperature of from about 400 to about 850F. and a pressure of from about atmospheric to 2000 pounds, theimprovement which comprises adding sulfur to said distillate in anamount such that the total sulfur is in a concentration at least equalto that expressed by the equation S=25.8N+0.07l, where S is sulfur inweight percent and N is nitrogen in weight percent, provided, however,that the total sulfur concentration is at least 0.2% by weight of saidpetroleum distillate,

4. The process of claim 3 further characterized in that the sulfur isadded as free sulfur.

5. The process of claim 3 further characterized in that the sulfur isadded as hydrogen sulfide.

6. The process of claim 3 further characterized in that the sulfur isadded as carbon disulfide.

7. The process of claim 3 further characterized in that the sulfur isadded as thiophene.

8. The process of claim 3 further characterized in that the sulfur isadded as mercaptan.

9. In the removal of nitrogen from naphtha containing nitrogen in aproportion to sulfur greater than hereinafter defined, by treatment withhydrogen and a catalyst comprising alumina-molybdenum sulfide-cobaltsulfide at a temperature of from about 400 to about 800 F. and apressure of from about atmospheric to 2000 pounds, the improvement whichcomprises adding sulfur to said distillate in an amount such that thetotal sulfur is in a concentration at least equal to that expressed bythe equation S=25.8N+0.071, where S is sulfur in weigh percent and N isnitrogen in weight percent, provided, however, that the total sulfurconcentration is at least 0.2% by Weight of said naphtha.

References Cited in the file of this patent UNITED STATES PATENTS1,852,988 Varga Apr. 5, 1932 2,392,579 Cole Jan. 8, 1946 2,393,288 ByrnsIan. 22, 1946 2,604,438 Bannerot July 22, 1952 2,692,226 Smith Oct. 19,1954

1. IN THE REMOVAL OF NITROGEN FROM A PETROLEUM DISTILLATE CONTAINING NITROGEN IN A PROPORTION TO SULFUR GREATER THAT HEREINAFTER DEFINED, BY TREATMENT AT PURIFICATION CONDITIONS IN THE PRESENCE OF A MOLYBDENUM CONTAINING CATALYST, THE IMPROVEMENT WHICH COMPRISES ADDING SULFUR TO SAID DISTILLATE IN AN AMOUNT SUCH THAT THE TOTAL SULFUR IS IN CONCENTRATION AT LEAST EQUAL TO THAT EXPRESSED BY THE EQUATION S=25.8N+0.071, WHERE S IS SULFUR IN WEIGHT PERCENT AND N IS NITROGEN IN WEIGHT PERCENT PROVIDED, HOWEVER, THAT THE TOTAL SULFUR CONCENTRATION IS AT LEAST 0.2% BY WEIGHT OF SAID PETROLEUM DISTILLATE. 